Explosion proof junction box

ABSTRACT

An explosion-proof and corrosion resistant junction box for electrical connection junctures and the like including a cap portion having a downwardly extending external screw portion, and a body portion having an internal screw portion. Both cap and body portions have a resilient, moisture resistant, polymeric coating bonded to the metal substrate. The cap and base portion coatings terminate in downward and upwardly extending relatively flexible flanges around their respective peripheries. The respective coated portions are adapted to threadably engage whereby the flange portions come into contact to provide an effective one-way vapor seal, and whereby the screw portions provide a path for gases from within to without the junction box. Hot gases under pressure within the junction box may pass along the path in said screw portions and through said one-way vapor seal, and, in so doing, become cooled to thereby prevent ignition or explosion of atmospheric gases near the junction box. The flange portions provide an effective moisture and vapor seal whereby corrosive vapors are prevented from corroding the outside surfaces or entering the junction box.

United States Patent 1191 Slocum [S4] EXPLOSION PROOF JUNCTION BOX [75]Inventor: Fred H. Slocum, Pittsburgh, Pa.

[73] Assignee: Robroy Industries, Verona, Pa.

[22] Filed: Aug. 30, 1971 [21] Appl. No.: 175,916

[52] US. Cl ..220/3.8, 137/525.l, 174/17 UA, v 174/50, 174/65 R, 215/56,220/44 R [51] Int. Cl. ..H02g 3/08, B65d 51/16, H02g 3/18 [58] Field ofSearch....220/3.2, 3.8, 3.92, 3.94, 44 R,

220/44 A, 46 R; 174/17 UA, 50, 65 R; 215/56; 137/5251, 525.3

Primary Examiner-JosephR. L eclair Assistant Examiner-Allan N. ShoapAttorney-Stanley J. Price, Jr.

1 51 Apr. 3, 1973 [57] ABSTRACT An explosion-proof and corrosionresistant junction box for electrical connection junctures and the likeincluding a cap portion having a downwardly extending external screwportion, and a body portion having an internal screw portion. Both capand body portions have a resilient, moisture resistant, polymericcoating bonded to the. metalsubstrate. The cap and base portion coatingsterminate in downward and upwardly extending relatively flexible flangesaround their respective peripheries. The respective coated portions areadapted to threadably engage whereby the flange portions come intocontact to provide an effective oneway vapor seal, and whereby the screwportions provide a path for gases from within to without the junctionbox. l-lot gases under pressure within the junction box may pass alongthe path in said screw portions and through said one-way vapor seal,and, in so doing, become cooled to thereby prevent ignition or explosionof atmospheric gases near the junction box. The

flange portions provide an efiective moisture and vapor seal wherebycorrosive vapors are prevented from corroding the outside surfaces orentering the junction box.

7 Claims, 5 Drawing Figures I 1 EXPLOSION PROOF JUNCTION BOX BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates to ajunction box for electrical connection or the like, and moreparticularly to an explosion-proof, corrosion resistant junction box.

2. Description of the Prior Art It is well known that explosion hazardsexist in many industrial atmospheres. Typical explosion hazards existwhere explosive gases such as acetylene, hydrogen, ether, gasoline,naphtha vapors, or the like, are present, and where a combustible dustis present, as in a chemical spray drying area. In order for a fire orexplosion to occur, a sufficient amount of inflammable vapors orcombustible dust must be present, a suflficient amount of combustionsupporting gas, such as air, must be present, and finally, an energysource must be present often, the required energy source for ignition isfound in electrical equipment or connections, and explosions within anelectrical conduit have caused general explo-' sions in the surroundingarea. Thus, it has become necessary to provide explosion-proofelectrical connections, such as'junction boxes and the like, to preventthe energy for explosive ignition from escaping into the combustibleatmosphere or explosive atmosphere. Explosion-proof electricalapparatus, such as a junction box, are designed and manufactured strongenough to contain an explosion and to prevent the escape of flame orexcess heat that could ignite the surrounding atmosphere. Suchapparatus'have not been gas tight, but have been designed to allow thecontrolled escape of gases. Certain electrical apparatus, such asjunction boxes, have been proposed having a ground joint or porous metalcomponent for permitting controlled escape of gases. Those devices,though providing a somewhat satisfactory explosion-proof apparatus, insome instances must be coated against corrosion when exposed to certaincorrosive vapors. Where the junction box is coated after installation,the gas escape passages are sealed by the coating. Where the junctionbox is precoated prior to installation and provisions are made for theescape of gas from the junction box, portions of the threads remainexposed to the corrosion vapor. v

This invention provides an improved junction box for electricalconnections that is both explosion-proof and corrosion proof. Moreover,the invention provides "an improved junction box of the type describedwhich is corrosion resistant under substantially all conditions, andwhich will effectively prevent corrosive vapors or dust" from corrodingthreads and reaching electrical components within the junction box.Moreover, the invention provides an explosion-proof junction box whichwill permit hot gases under pressure within the junction box to escapetherefrom in a manner whereby those gases are effectively cooled and thepressure effectively dissipated while preventingcorrosive vapors fromcorroding threads and entering the internal portion of the junction box.

SUMMARY OF THE INVENTION This invention provides an explosion-proofjunction box for electrical connection junctures, and the like,including a body portion and a cap portion adapted to be threadablyengaged thereto. Preferably, the cap portion has a downwardly extendingexternal threaded portion, and the body portion has an internal threadedportion for receiving said downwardly extending external threadedportion of the cap. Both the cap and body portions. have a resilient,moisture resistant polymeric coating, preferably a polyvinyl chloride(PVC) coating. The cap and body portion coatings terminate respectivelyin downwardly and upwardly extending flanges around their respectiveperipheries. The coated portions are adapted to be threadably engagedwhereby the flange portions come into sealing contact to provide aneffective seal for the threaded portions of the junction box against thecorrosive vapors and yet provide a path for gases to escape from withinthe junction box. Should an explosion occur in an electrical conduit,the hot gases under pressure within the junction box may pass along thepath in said screw portions and through said one-way seal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a top plan view of ajunction box according to the invention.

FIG. 2 is a sectional view taken along the line Il-II of FIG. 1.

FIG. 3 is a more detailed view of the threaded joint between thejunction box body portion and cap portion illustrated in FIG. -2.

FIG. 4 is a view of the threaded joint according to the inventionwherein gases are escaping from the junction box.

FIG. 5 is a view of the threaded joint in a junction box illustratingthe preferred construction of the resilient flange seal according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 andFIG. 2, a junction box according to the invention is shown having a capportion 10 and a body portion 20. Body portion 20 has one or moreinternally threaded pipe-coupling members 30. Coupling members 30 areadapted to threadably receive and threadably advance wire-carryingconduit pipe (not shown) for bringing electrical wires into the junctionbox of the invention.

Both cap portion 10 and body portion 20 are provided with a moistureresistant polymeric coating 40. Coating 40 preferably comprises amoisture proof, chemical resistant, impact resistant polymericcomposition. Most preferably, coating .40 comprises a polyvinyl-chloridecoating (PVC), but equivalent compositions may be employed. For example,impact resistant nylon, polypropylene, polyurethane, or polyethylenecoatings are suitable. Coating 40 protects cap 10 and body 20 portionsof the junction box from corrosion damage due to corrosive vapors.

Coating 40 extends beyond the respective peripheries of cap portion 10and body portion 20 and thereby forms flanges 42 and 44 respectivelythereon. Each of I extends beyond coupling member 30 for providing amoisture resistant sleeve 41 for sealably engaging a conduit pipe inmember 30. In that manner corrosive vapors are prevented from enteringthe junction box of the invention through conduit coupling connections.

Cap portion is provided with a downwardly extending external threadedportion 12, and body portion is provided with an upwardly extendinginternal threaded portion 22. Thus the polymer coated cap and bodyportions may be threadably engaged through threaded portions 12 and 22in a manner whereby cap portion 10 may be downwardly (as shown) advancedinto body portion 20. Lugs 25, or the like, may be provided for-aidingin turning cap 10 within body portion 20. Advancing of cap portion 10into body portion 20 is continued at least until flange portions 42 and44 on the respectiveperipheries of cap portion 10 and body portion 20come into sealing contact. In that fashion an effective resilient,corrosive vapor seal is provided for the junction box of the invention.The seal formed by flanges 42 and 44 will effectively prevent the entryof corrosive vapors into the junction box to thereby protect the threadsfrom corrosion by the corrosive vapors. In the most preferred form ofthe invention shown in 1 FIG. 5, flanges 42 and 44 are downwardly andupwardly extending, respectively, whereby a resilient seal is formedhaving a rather broad sealing surface. As best shown in FIG; 5,threadably advancing cap portion 10 downwardly into body portion 20 willcause ever increasing portions of the contacting surfaces of resilientflanges '42 and 44 to come into contact in sealing relationship. I

. Capportion 10 and body portion 20 are adapted to a be threadablyengaged whereby their respective threaded portions'12 and 22 provide apath for gases from within to without the junction box. As shown in FIG.3, downwardly extending external threaded portion 12 of cap portion 10includes threads 14, and upwardly extending internal threaded portion 22of cap 20 includes threads 24. Threads 14 are somewhat content, andhence temperature, of the hot gases to a degree. Moreover, the rapidexpansion ofthe hot compressed gas after passing through theseal intothe atwithin the junction box may pass. It should be noted here thatthreads 12 and 14 maybe scored along the outer edges thereofforproviding an additional escape path or paths for gases within thejunction box. Scoring or grinding of the'u'ppermost (as shown) thread isespecially preferred. While passing along the helical path, hot gasesare effectively. cooled by. contact with the cooler metal threads. Aftertraveling the entire course of threads'the hot gases may pass withoutthe junction box through the seal between flanges 42 and 44 as shown inFIG. 4. As will be. recalled,-flanges 42 and 44 comprise aresilient-material and internal gaseous pressure will cause the sealtobreak, as is shown, thereby allowingthe gasesto escape to thesurrounding atmosphere. It should further be noted that work, in aphysics sense, is required'ofthe hot gas to open the seal. The workrequired necessarily reduces the energy mosphere will further tend tocool gas-passing through the seal. After atmospheric pressure outsidethe seal is greater than or equal to the pressure within the junctionbox, plus the pressure required to break the seal between flanges 42 and44, the resilient seal again closes to prevent vapors or dust fromentering the junction box.

In the embodiment shown in FIG. 3 the surface of a cap flange portion 11and the surface of a body flange portion 21 are ground or roughened. Inthat fashion a passageway comprising an abutting ground surface jointbetween cap flange 11 and body flange 21 is provided through which gasesmay pass. In the alternative, the flange surfaces need not be ground solong as a passageway, such as passageway 50,. is provided through whichgases may pass to the seal formed of flanges 42 and 44 (FIGS. 4 and 5).In an additional alternative, a porous metal ring (not shown) may beprovided between cap portion 10 and body portion 20 through which gasesmay'pass and be further cooled thereby. Both the ground flanges andthe'po'rous metal ring are protected against the corrosive vapors by theflanges 42 and 44.

According to the provisions of the patent statutes, I have explained.the principle, preferred construction and mode of operation of myinvention and have illustrated and described what I now consider torepresent its best embodiment. However, it should be understood that,within the scope of the appended claims, the invention may be practicedotherwise than as specifically illustrated and described.

Iclaim: v I

1. An explosion-proof junction-box for electrical connection junctures,or the like, including a cap portion and a body portion, said capand'body portions having a resilient, moisture resistant polymericcoating, said coating extending beyond the respective peripheries ofsaid cap and said body portions whereby respective resilient flanges areformed thereon, said cap and body portions including threaded portionsfor threadably advancing said cap portion into said body portion wherebysaid .resili'ent flange portions come into sealing contact to provide aneffective one-way vapor seal for said junction box to prevent the flowofcorrosive 'vaporsinto the threaded portions of said cap and bodyportions and permit the outflow of gas from said junction box throughsaid threaded portions.

2. The explosion-proof junction box as set forth in claim 1 wherein saidrespective resilient flange portions comprise a flange portion extendinggenerally downwardly of said cap portionand a flangeportion extendinggenerally upwardly of said body portion.

3. The explosion-proof junction box as set forth in claim 2 wherein saidpolymeric coating comprises a polyvinylchloride film coating.

4. The explosion-proof junction box as set forth in claim 3 wherein saidthreaded portions comprise an external threaded portion extendingdownwardly of said cap portion and formed integrally thereof, and aninternal threaded portion formed integrally of said portion.

5. The explosion-proof junction box as set forth in claim 4 wherein saidexternal threaded portion and said through which gases may pass betweensaid ground and lo abutting surfaces.

7. The explosion-proof junction box as set forth in claim 1 wherein saidbody portion includes one or more pipe coupling members extendingtherefrom for receiving a wire bearing conduit, and wherein said coatingextends beyond each of said coupling members for providing a moistureresistant sleeve for 'sealably engaging said conduit.

1. An explosion-proof junction box for electrical connection junctures,or the like, including a cap portion and a body portion, said cap andbody portions having a resilient, moisture resistant polymeric coating,said coating extending beyond the respective peripheries of said cap andsaid body portions whereby respective resilient flanges are formedthereon, said cap and body portions including threaded portions forthreadably advancing said cap portion into said body portion wherebysaid resilient flange portions come into sealing contact to provide aneffective one-way vapor seal for said junction box to prevent the flowof corrosive vapors into the threaded portions of said cap and bodyportions and permit the outflow of gas from said junction box throughsaid threaded portions.
 2. The explosion-proof junction box as set forthin claim 1 wherein said respective resilient flange portions comprise aflange portion extending generally downwardly of said cap portion and aflange portion extending generally upwardly of said body portion.
 3. Theexplosion-proof junction box as set forth in claim 2 wherein saidpolymeric coating comprises a polyvinylchloride film coating.
 4. Theexplosion-proof junction box as set forth in claim 3 wherein saidthreaded portions comprise an external threaded portion extendingdownwardly of said cap portion and formed integrally thereof, and aninternal threaded portion formed integrally of said portion.
 5. Theexplosion-proof junction box as set forth in claim 4 wherein saidexternal threaded portion and said internal threaded portion includerespective helical threads having differing dimensions.
 6. Theexplosion-proof junction box as set forth in claim 5 wherein said capand body portions include respective cap flange and body flangeportions, and wherein said cap flange and body flange portions may abut,each of said cap flange and body flange portions having a ground surfacefor providing a passageway through which gases may pass between saidground and abutting surfaces.
 7. The explosion-proof junction box as setforth in claim 1 wherein said body portion includes one or more pipecoupling members extending therefrom for receiving a wire bearingconduit, and wherein said coating extends beyond each of said couplingmembers for providing a moisture resistant sleeve for sealably engagingsaid conduit.